1. Field of the Invention
The present invention relates to a fuel cell system, particularly relates to a fuel cell system devised to be useful as a power source of a small-sized electronic apparatus of a portable apparatus or the like by preventing a deterioration in a single cell of a fuel cell by polarization reversal or overload.
2. Description of the Related Art
In recent years, power consumption of a portable apparatus represented by a portable telephone is more and more increased in accordance with high function formation of the apparatus and an increase in a capacity of a power source poses a serious problem. Under such a situation, attention is attracted to a fuel cell as a small-sized energy power source having a high energy density.
A fuel cell is constituted by interposing an electrolyte by two kinds of electrodes, and electricity is generated by oxidizing a fuel of a hydrogen or methanol or the like by a fuel pole and reducing oxygen in the atmosphere by an oxygen pole. In fuel cells, a solid polymer type fuel cell (PEFC) is expected to be applied as a power source for a portable apparatus since the cell is capable of power generation at around room temperature provided with a high output density and can be downsized.
When a fuel cell is used as a power source, a practical operating voltage of a single cell of the fuel cell is around 0.5V. Hence, in order to produce a practical voltage necessary for a load, a predetermined high output voltage is produced by connecting a necessary number of the single cells in series.
Although in this way, by connecting the single cells of the fuel cell in series, a fuel cell having a high voltage and a high output can be provided, when the plurality of single cells are connected in series to use, there poses a problem that a power generating function of the fuel cell as an assembly of the single cells is deteriorated owing to a variation in an output of each single cell. Because a single cell having the lower power generating function constitutes a resistance component to reduce the output of the fuel cell. Therefore, in order to restrain a variation in outputs of respective single cells, there is proposed a fuel cell devised to control a fuel supplying method by using auxiliaries or the like (refer to. for example, JP-A-06-103998 page 3, FIG. 1)